1. Field of the Invention
The present invention belongs to relay protection and automation of electrical engineering field, and in particular to a busbar differential protection applicable for various voltage ratings based on a novel method of synchronous sampling and transmission technology.
2. Background of the Invention
A busbar is one of important devices of power plants and substations in electrical power system, playing a role of merging and distributing of electrical power. Its overall length is just dozens or hundreds of meters, but a short circuit fault occurs due to a great amount of connected devices, the complicity of electrical wiring, aging of device insulation, contamination and lightning strike; meantime, man made three phase fault arises because of frequent operations and mis-operations of an operator. Therefore, the short circuit fault of busbars still accounts for a certain percentage in the electrical power system. Furthermore, its property of fault is generally severe, doing a great harm to the electrical power system. In view of this, it is demanded that busbars with 110 kV or higher voltage ratings and important busbars with 35 kV voltage ratings be equipped with busbar differential protection.
Today's normal busbar differential protection home and abroad is to introduce currents on all intervals into a busbar differential protection device, which accomplishes synchronous sampling of analog signals and differential logic judgment. Such method requires access to large amounts of secondary cables. The cables need not only large investments, but also lots of constructions on site, which is hard to be granted in smart substations.
It is noted that, as used in this specification and the appended claims “PT” refers to potential transformer.
As used herein, “OLT” refers to optical line terminal.
As used herein, “EPON” refers to Ethernet Passive Optical Network.
Nowadays in smart substations, GPS synchronous technology is largely used, in which timestamps are added to sampled current and voltage data, in doing so, the differential current on the busbar at the same time is obtained. But the drawback along with this method is obvious, because such busbar differential protection has strong dependency on GPS signals, and it will be out of operation without GPS synchronous signals. At the same time, GPS data will occupy most of the channel resources.